A variety of electro-optic devices are utilized in scientific, commercial, industrial and consumer applications. Semiconductor multiple quantum well (MQW) modulators represent a type of electro-optic device possessing a broad range of application capabilities. Semiconductor MQW modulators generally operate with incident light normal to the plane of the device. Such devices are well known in the art are of considerable interest because they are the fundamental elements for spatial light modulators, and have the potential for functioning as high speed dynamic range devices that can be integrated with detector and control electronic circuits.
Prior research on normal incidence multiple quantum well light modulators has concentrated on amplitude modulation, relying on a sufficient difference in the absorption coefficient between the on/off states at the operating wavelength to achieve useful contrasts. Such changes in the absortion coefficient have typically been effected by the so-called quantum confined Stark effect (QCSE), Wannier Stark localization, or photo induced excitonic absorption saturation. Note that in general, the Stark effect involves the splitting of atomic spectral lines as a result of an externally applied electric field. The Stark effect has been of marginal benefit in the analysis of atomic spectra, but has been a major tool for molecular rotational spectra.
An example of a spatial light modulator which utilizes a uniaxially strained multiple quantum well device is disclosed in U.S. Pat. No. 5,381,260 entitled, “Uniaxially Strained Semiconductor Multiple Quantum Well Device Using Direction-Dependent Thermal Expansion Coefficients in a Host Substrate,” which issued to Ballato et al on Jan. 10, 1995. U.S. Pat. No. 5,381,260 is incorporated herein by reference. U.S. Pat. No. 5,381,260 discloses a spatial light modulator, which utilizes a uniaxially strained multiple quantum well (MQW) structure with an anisotropic absorption to rotate the polarization of light normal to the MQW structure. The anisotropy, which produces this rotation, is the result of a thermally induced in-plane anisotropic strain. The MQW light modulator based on this process possesses a high contrast ration of 7000:1 and increased speed as compared to other similar modulators.
One of the problems associated with spatial light modulators, such  as that disclosed in U.S. Pat. No. 5,381,260, is that it is difficult to achieve proper anisotropic strain without the removal of the semiconductor substrate upon which the spatial light modulator is formed, or without using another substrate. Additionally, bonding and lift-off procedures offer additional and often expensive complications to the manufacturing process. The present inventors have thus concluded, based on the foregoing, that a need exists for an improved method and apparatus for inducing anisotropic strain in quantum well structures and devices thereof. If an efficient technique for inducing anisotropic strain can be implemented, it is believed that a wide variety of improvements can be achieved, including, but limited to, high contrast light modulators for real time object and pattern recognition and infrared detection and imaging. The present inventors thus believe that the invention disclosed herein addresses these long-felt needs.